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chuckg5 · 08-12-2022, 21:36

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

smac999 · 08-12-2022, 21:38

you should be checking every couple months. that battery will likly be damaged if it was empty

ranger58sb · 09-12-2022, 05:02

Quote:

Originally Posted by chuckg5

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

All probably wasn't really working fine; batteries were probably gradually degrading over all that time... and you finally reached the point where it became noticeable.

Agree; check every couple months (or more often, if necessary), add water as required.

You have four 12V and two 6V batteries in the same bank?

-Chris

boatpoker · 09-12-2022, 06:09

Electrolyte can disappear quite quickly. Continuing to charge a battery with no or low electrolyte is dangerous. I have many photos of batteries that have exploded due to this. We do battery checks every Friday.

Where do you think all the sulphuric acid from these batteries went when they exploded ?

**boatman61** · 09-12-2022, 07:21

I'd suggest you check your car battery now, if it's a lead/acid.

GrowleyMonster · 09-12-2022, 07:21

Quote:

Originally Posted by chuckg5

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

So you are running 54 volts?

But as for the dry 6v battery it might be salvageable. Isolate that one, fill it just until the plates are covered, and charge it. Check the water. The battery should make water when it charges. If it takes a full charge, go ahead and top it up. Discharge it through a resistor or other load, and do another charge cycle. Then you should equalize. This is a controlled over-charge. Consult your battery maker's website for the correct equalizing voltage because NO "smart" charger will do a true equalization. The voltage simply will not go high enough. I use a large Variac and a rectifier from an old stick welder. Like I said it requires monitoring. Monitor voltage, battery temperature, and charging current. I use a shunt ammeter for current. Actually I have a 25 amp direct series connection ammeter but I haven't used that yet. There will be significant gassing. This should be done on deck or on the dock, nobody smoking or burning or welding nearby.

I ran a 48v bank of 6v GC-2 golf cart batteries on my e-boat and I equalized every couple of months and got 8 years of service out of them. I usually equalized the entire bank at 64 to 65 volts. As the batteries aged I started equalizing them individually at around 8.1 volts. The knob on the Variac must be adjusted to maintain the desired voltage.

Assuming your batteries are true deep cycle, in lieu of recommendations from the manufacturer's website, you might go by Trojan's recommendations. 2.7v per cell for equalizing. In fact the Trojan website has a lot of great information guidelines and tips on using deep cycle batteries.

Most "marine" batteries are not true deep cycle batteries. They are a compromise between good engine start performance and deep cycle storage performance. Just keep in mind that deep cycle and marine batteries are two similar but different critters.

Most yachties do not bother with equalizing or even know how to do it or even are aware that it is a thing. If the boat is taken out often, it isn't so important. The motion of the boat helps to prevent stratification of the electrolyte. One of the things that equalizing does is mix up the electrolyte.

At any rate, that particular battery needs special attention if it is to be saved and not cause problems being in parallel with the other 6v and in series with your 12v batteries.

Why the odd voltage? EP setup? Honestly I would just run 48v, which is 4 12v batteries in series. If you are going to go over 50V then you may as well go up to at least 96v for greater efficiency.

As for what could have made that battery go dry, hard to say from here. High current passing through that battery, maybe. Bad connections on its mate. Shorted cell or two. General neglect or mistreatment. Manufacturing defect. End of life performance issues. But if you replace it, also replace the other one that you have in parallel.

<EDIT> Now would be a good time to clean and retighten and grease all of your battery connections, and wipe down the case tops.

boatpoker · 09-12-2022, 07:34

Quote:

Originally Posted by boatman61

I'd suggest you check your car battery now, if it's a lead/acid.

Ask any auto mechanic about that. Ignorance is not bliss.

Google this phrase "lead acid battery explosion images"

team karst · 09-12-2022, 09:00

every molecule of water gets you a molecule of H2 gas.
with a 1000 to 1 volume ratio.

maybe an overcharge/overvoltage situation too. Definitely check the charge V.

Cheechako · 09-12-2022, 09:06

Quote:

Originally Posted by chuckg5

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

Put the battery set on a charger for a few hours. Feel each battery. If one battery is hot, it has an internal short. Yes it happens with new batteries. I have had two in 3 decades of sailing this happened to. One was a big, brand new 8D battery. I was already on the way to Mexico so never did get a warranty. Ended up using cheap Mexican car batteries in it's place.

**Jammer** · 09-12-2022, 09:18

I would guess it was a shorted cell though usually I would expect that to have affected both 6v batteries in the string. As Cheechako writes, shorted cells are fairly common in FLAs.

boatpoker · 09-12-2022, 09:38

Quote:

Originally Posted by Jammer

I would guess it was a shorted cell though usually I would expect that to have affected both 6v batteries in the string. As Cheechako writes, shorted cells are fairly common in FLAs.

I'm not so sure. I've never seen an internal short without a significantly swollen or distorted case.

If you see swelling like this, disconnect it right away. Ignoring this could lead to something more dramatic.

**Jammer** · 09-12-2022, 13:14

Quote:

Originally Posted by boatpoker

I'm not so sure. I've never seen an internal short without a significantly swollen or distorted case.

Depends how soon you catch it.

wholybee · 09-12-2022, 13:29

I expect that what you mean is that you have 4 12V batteries in parallel, and 2 6V in series, and that the pair of 6V is in parallel with the 4 12V.

When I was working my FLA bank hard in the tropics, I had to add water every 3 weeks. Even not working them hard, I had to top off every couple months. Until you learn the pattern, you should check them weekly. That 6V battery is probably toast.

What went wrong, aside from going many months too long without checking it, is that you have a bank with mixed sized, and probably aged, batteries. That is not recommended. It can be done, but wear on the batteries will be uneven, and require more checking and watering, and also the expectation of a reduced life.

What you need to do now is check everything. The bank still works because you have 4 12V batteries that are at least mostly working. But with a failed 6V battery, they probably are not charging properly. So that means disconnect it all. Individually fully charge every battery, check the water level, and then measure the gravity of every cell in every battery. Let them sit 24Hrs, then check the gravity and voltage again. Almost certain the one 6V is done. You might find the other 6V is also bad, or that one or more of the 12V has a problem. Probably, the 12V are fine, but it is really important that you check them thoroughly now that a battery in the bank failed.

wholybee · 09-12-2022, 13:32

Quote:

Originally Posted by boatpoker

I'm not so sure. I've never seen an internal short without a significantly swollen or distorted case.

If you see swelling like this, disconnect it right away. Ignoring this could lead to something more dramatic.

The swelling comes after, from overcharging what with a shorted cell is only a 10V nominal battery. But before you found it, the battery had a shorted cell and wasn't distorted.